Storage systems, due to the need to handle large volumes of data, have become larger in scale and more complex in recent years. For this reason, there is demand for storage systems that can be managed easily and used efficiently. One prior art that meets this demand is thin provisioning technology. In this technology, the storage system constructs a virtual logical volume (called a “virtual volume” hereinafter) that does not comprise a physical storage area. The storage system then provides the virtual volume to a host computer. The host computer carries out a data write request to a virtual page that makes up this virtual volume. The storage system allocates a pool page from a pool configured from multiple pool pages to the virtual page targeted by the data write request. The pool comprises either one or multiple physical storage areas (referred to as a “disk volume” hereinafter). Each disk volume is partitioned into two or more pool pages. The disk volume comprising the pool may be a substantial logical volume configured based on one or more storage media (for example, a RAID group configured using multiple storage media), or a virtual logical volume to which is associated a logical volume of a storage system external to the storage system.
In accordance with this technology, the storage system-provided volume capacity can be efficiently used, and the volume capacity can be appropriately designed.
The disk volume is generally configured from storage media of the same performance. However, the frequency with which respective virtual pages are accessed is normally not the same, and frequently accessed virtual pages are mixed together with infrequently accessed virtual pages. For this reason, for example, in a case where the disk volume is configured using only a high-performance storage medium, an excess of performance will occur with respect to a virtual page with a low access frequency. By contrast, in a case where a pool is configured using only a low-performance disk volume, a shortage of performance will occur with respect to a virtual page with a high access frequency.
One method for solving this problem is disclosed in Patent Literature 1. According to Patent Literature 1, a single pool is configured using multiple disk volumes having different performance (typically, access performance), and based on the access frequency of each virtual page, a pool page allocated to a virtual page and data stored in this pool page is reallocated to a pool page of a disk volume comprising the ideal performance. The performance of the disk volume depends on the performance (typically, access performance) of the storage medium constituting the basis for this disk volume.